engine won't start and I have spark! Video Included

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sergman89

New Member
Jul 7, 2012
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Hey guys so here is the full story made short.

Bought a kit and installed it then after breaking in I over tightened the head bolt and messed up the lower engine case.

I bought a new lower engine from thatsdax.com but it was a different crank arm size so it would lock up.

then I got a new upper engine to fit the longer crank arm and the correct piston as well so it rotates freely now.
The metal wheels inside the lower engine have nicks in the metal from trying to get the wrong piston to start in the engine.

I sanded the head (where the spark plug goes) down so it was perfectly level, since it was a little warped.

Replaced the CDI and Spark Plug.

Then I replaced the magneto even though I had spark.

as you will see in the video I rigged the bike up so I could use a drill to rig up a Pull start kinda deal. While doing this at first I got a few shots of Fire out of the open Exhaust hole. So I opened the choke a little to see if it would help and twisted the throttled But it didon't shoot fire again or start up.


Here is the video so you can see and hear it and maybe it'll make it easier for you to help
https://youtu.be/cJ-JEMiey4E
 

Davezilla

New Member
Mar 15, 2014
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Have you checked to see if your magneto rotor is installed correctly? it will go on backward and be so far off timing it'll never fire the cylinder. To check this, remove the mag cover if it's installed, set your piston to TDC and check to make sure your mag rotor is horizontal on the crank, the cutouts should be positioned at 12 and 6 o clock, if it's sitting on there slanted it's on backward.

Next possible cause is what's your gas/oil mix ratio at? a new engine with 16:1 mix will be very difficult to start at first, try it at 32:1 and it's perfectly safe to do so on a new engine.

Also, is your fuel nice and fresh? Today's gasolines with 10% alcohol tend to degrade rather quickly, if your mix is over a month old, try making up a new batch.

Check your head gasket for leaks, even if it feels like you got compression, a small leak here can make it very difficult to start, some stock heads and cylinders are pretty far from being perfectly flat and even a new gasket won't seal unless you ture up the head and sometimes the cylinder deck.

Finally, i saw the video you posted and your spark looks to be a bit on the weak side, try a smaller gap on the plug, also do an ohm check on the mag coil and make sure you got at least 350 or so ohms resistance, if you got like 500 ohms, don't worry, this just means you got a good strong coil... The magnets can also degrade if stuck to a piece of steel for a good amount of time or if they were stored stuck to other magnets for an extended period, some magnets are just weak from the get go because they weren't magnetized strong enough. The magnet should be rather strong, like strong enough to make it difficult to pull off a piece of steel or. Other things that can kill the magnet is if it was rubbing against the mag coil pickup arms from being installed with one side touching.

The spark it's self should be bright enough to see outside in plain daylight and be mostly white with a little blue in it, if it's pale blue or has any hint of orange in the spark it's self it's probably too weak to fire under cylinder pressure...

That's all I can think of right now but hopefully this helps some.
 

sergman89

New Member
Jul 7, 2012
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That's all I can think of right now but hopefully this helps some.
thanks I'll give this a shot asap. When I check my Magneto I set my multimeter to 2k and it gives me a fluctuation from 307-312. I put Red stick to Blue wire and Black to Black since my magneto doesn't have the white wire. Was this the correct way to check?
 
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Davezilla

New Member
Mar 15, 2014
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Yup... there's no polarity on the magneto wires until it's installed, then the black side is also tied to ground so it doesn't matter which meter lead goes where, just be sure the magneto is unplugged from the cdi when measuring to get the most accurate reading.
307 to 312 is a bit on the low side but should still be able to spark strong enough to fire the engine up. I've seen them as low as 325 ohms and work perfectly so that little bit shouldn't be preventing a spark under cylinder pressure.
 

Davezilla

New Member
Mar 15, 2014
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Do you have a compression tester? this would be a good way to detect a leaky head gasket without having to remove the head. Stock compression should be around 100 psi. Check compression by caosting with the clutch out (unless you got a pull starter) and the throttle opened up to full throttle, if it reads really low, squirt a few drops of oil into the cylinder to see if it improves, if it improves really nicely, there's a leak at the head gasket or your rings have a bad seal.
 

Davezilla

New Member
Mar 15, 2014
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San Antonio Texas
I'm falling asleep over here so I'm going to bed now... Others should be online to help out, but if not, and you still can't get it started I'll be back in the morning for a short time... Hope you get it figured out.
 

sergman89

New Member
Jul 7, 2012
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So a piston ring broke inside and scored the piston and the cylinder head. The scratch on the inside of the cylinder head is about 1.5 inches long.

it even scratched the gas reciever chamber inside the cylinder. Can I replace the piston head or do I need a new cylinder head too?
 

Davezilla

New Member
Mar 15, 2014
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Yup... What he said...^^

You can usually get a cylinder/piston, and rings combo from most sellers for $30 to $45 depending on the seller and the quality of the parts. i got a setup like that from BGF on ebay last summer for $25 and it came with a cylinder, piston, rings, and an intake manifold. I never used the cylinder since it was one of those with the cat eye transfers and they're not that great for performance. These parts will get ya back up and running quickly and cheaply tho.
 

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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I agree with Davezilla, but honestly, 99.999% of chinadoll owners will never notice any difference unless they plan on porting the jug. BGF is good for cheap stock stuff for a cheap stock build, and is okay for porting as well unless you really know your stuff and want the best start available.
Most riders would never know which engine they had without the little riveted nametags....
 

2door

Moderator
Staff member
Sep 15, 2008
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Littleton, Colorado
Sergman89,
I can't add anything to the advice you're getting from two of our most respected members. Listen to these two gentlemen and they'll get you back on the road.
You're fortunate to have them helping you.

Tom
 

MotorBicycleRacing

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Jul 28, 2010
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So a piston ring broke inside and scored the piston and the cylinder head. The scratch on the inside of the cylinder head is about 1.5 inches long.

it even scratched the gas reciever chamber inside the cylinder. Can I replace the piston head or do I need a new cylinder head too?
Damn, just buy a complete motor.
Then play with your other one as a learning experience.
Cylinders and heads are two different parts and What is a "gas receiver chamber?"
 

Davezilla

New Member
Mar 15, 2014
2,705
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San Antonio Texas
Damn, just buy a complete motor.
Then play with your other one as a learning experience.
Cylinders and heads are two different parts and What is a "gas receiver chamber?"
I'm assuming hes talking about the combustion chamber... and I'm sure he can get back up and running simply by changing a few simple parts. Its cheaper and not that hard to do even if its someones first time, these engines are about as simple as it gets and I see nothing wrong with someone learning on their running engine if they cant buy a complete engine due to budget or would just rather fix what they got. I never change the whole engine unless there's bottom end or crank damage/wear.

Pretty much anyone who can install a kit successfully can handle something like swapping out a jug and piston... besides they got the forum and youtube to help out if they get stuck anywhere.
As far as terminology on these parts, that's easy to learn as ya go if someone is new to all this... I know the guy got some of this wrong but its not that hard to walk someone who wants to learn their way thru this....